The crossword solution for the term 'CRACK A SMILE' is GRIN, which is a four-letter word. A GRIN is a facial expression that is usually associated with happiness and amusement. It is characterized by a wide smile that often shows the teeth and may also involve a laugh or chuckle. Grinning is a common response to something funny or enjoyable, and it can also be used to express friendliness or appreciation.